Synovial membranes of patients with RA contain large numbers of T and B lymphocytes. Currently, RA is considered to be an antigen-driven disease, in which a T cell-dependent B cell response to foreign or self antigens occurs among genetically predisposed individuals. Many studies have attempted to analyze the clonality of the T and B cell compartments in joints of RA patients. Most of these studies have examined T cells or B cells, but not both, and have focused on only one component of the antigen receptor [T cell receptor (TCR) a or b chains or immunoglobulin (Ig) heavy or light chains]. Furthermore, most studies have focused on chronically inflamed tissue at one point in time. The antigenic specificity of the majority of antibodies produced in RA synovium, especially early in disease, remains unknown. To assess the clonality of the T and B cell response in early RA synovium, they will perform small needle arthroscopic synovial biopsies on individuals with and without the RA susceptibility MHC class II haplotype. They will utilize single cell PCR to amplify and sequence TCR Vb and Ig VL transcripts from synovial and circulating cells likely to be important in the pathogenesis of the disease (IL-2R+/CD4+ T cells and plasma cells/activated B cells). Ig heavy chains of cells and TCR a chains of clonally expanded B and T cells, respectively, will then be sequenced to determine TCR a/b and Ig H/L pairing and to verify clonality. The degree of clonality of the synovial T and B cell responses will be reexamined 1 and 3 years later. Clonally expanded Ig heavy and light chains from early synovium will be cloned into eukaroytic expression vectors and complete recombinant human antibodies expressed in vitro. These antibodies will be tested for reactivity against antigens potentially important in the initiation or propagation of RA, including IgG Fc, type II collagen, and E. coli heat shock protein dnaj. The antibodies will also be used to screen a combinatorial library of peptide fragments, thus enabling screening without a preconceived bias about the identity of the antigen. These studies should serve as a reference for future studies of abnormal immune responses, provide insight into antigens that cause RA, and may identify targets for therapeutic intervention.